Quick Tech With Marlan Davis
Effective in-vehicle torque converter stall speed is defined as the rpm the engine can reach with the brakes locked and the transmission in gear before the drive wheels turn. Converter stall speed must be high enough to put the engine into the torque range where it can most efficiently launch the car. If converter stall speed is too low, the car will be lazy leaving the line; if too high, there’ll be excessive high-gear slippage—either case adds time to your e.t.
Engine builders use car weight and dyno data to aid selection. The converter is also matched to the transmission’s gear ratios. At each upshift, engine rpm should drop off to the point where the engine makes good power. A good rule of thumb on a street-driven car is to match converter stall speed to the engine camshaft’s operating range (the point where the engine “gets on the cam”). Racers should select stall speeds close to the engine torque peak.
Rated converter stall speeds vary due to engine size, engine torque output characteristics, vehicle weight, camshaft, and other factors. A large cubic-inch engine will raise a given converter’s stall speed. Engines that produce more low-end torque cause a given converter to stall at a higher rpm. A heavy car with large diameter tires will raise effective stall speed as installed in the vehicle. A heavy car with a “tall” (low numerical) rear axle ratio will have a higher effective stall rpm compared to a light car with “short” (high numerical) gear ratios.
TCI [ A typical TCI 10-inch StreetFighter converter is designed to work best with 280- to 300-degree advertised duration cams, 3.55–4.56:1 rear gears, and higher than stock compression ratios. Rated stall is 3,000–3,400 rpm in a typical small-block, but 3,400–3,600 rpm in a big-block. PN 142200, shown here, fits 1967–1982 727 TorqueFlites with a 24-spline input shaft.